Compared to the business they used to with the Sims, free to play makes it much, much harder to break even. You're hoping to monetize more off of a smaller percentage of your players. 95% of people will never pay in a free to play game, and the Sims games would sell over 10 million units each, handily, plus expansions. But I know that plenty of people would pirate the expansions, so EA probably sees that as a threat that they need to lock behind an internet connection in a server-based game, and they'll likely destroy the series' profitability in the process.